| Currently,the blueberry preservation technology has not completely solved the problems of surface damage and moldy during storage and transportation of fresh blueberries in China.Besides,sodium alginate(SA)has good film-forming and cyclolipopeptides(CL)from Bacillus subtilis is an amphiphilic substance with antibacterial effect.This study proposed that CL and SA could be made into a berry coating film that was easier to clean,to explore the effect of the film on the preservation of blueberries and the influence of CL on the film-forming performance of SA.The SA solutions combined with different concentrations(0%,1%,3%)of CL(SA-CL,SA-CL1,SA-CL3)were coated on the surface of blueberry.The physiological indicators of blueberries during storage were measured,and the film-forming properties(tensile strength,elongation at break,water vapor permeability,contact angle and solubility in water)were measured.The results are as follows:(1)The SA-CL films had a good fresh-keeping effect on post-harvest blueberries.The physiological indicators of blueberries treated with SA-CL films were significantly better than those of the control group during storage,and as the concentration of CL increased,the freshness preservation effect was more significant.On the 20 th day of storage,the total fungal colony of blueberry surface in the control group and SA-CL3 group were 5.5 × 104 and 2.5 × 103 CFU / g,respectively.This result was mainly due to the significant antibacterial effect of CL,which combined with SA can greatly reduce the total fungal colony on the surface of blueberries.The weight loss of blueberries in the SA-CL3 group was 4.4±0.16%,which was significantly lower than that of control group(12.7±1.07%).The softening of blueberry fruits during storage was delayed by coating,and the respiration rate was significantly decreased compared with the control group.(2)The stomata of blueberries were observed by SEM.After coated with SA-CL,the stomata of blueberry surface were covered,which inhibited the respiration and water loss of blueberries,effectively reduced the respiration rate and weight loss,and delayed the fruit softening.(3)The CL can affect the film-forming properties of SA.As the concentration of CL increased,the mechanical properties(tensile strength and elongation at break)of the films became weakened,and the water vapor permeability reduced from 684.22±0.87 g/m2/day(SA-CL0)to 398.10±0.87g/m2/day(SA-CL3),the contact angle and water solubility increased to 33.79±1.49° and28.92±1.48%,respectively.These results were mainly due to the fact that CL contain hydrophobic fatty acids.The addition of CL reduced the surface hydrophilicity of the film,and the lower watervapor permeability can inhibit the transfer of water between the blueberry surface to the environment.(4)Thermogravimetric analysis(TGA),X-ray diffraction(XRD),and Fourier transform infrared spectroscopy(FT-IR)were used to analysis the interaction mechanism between CL and SA.With the increasing concentration of CL,the thermal stability of the film was decreased and the peak at 13.4°was absent,while the intensity of peaks at 21.6° and 41.1° decreased with increasing CL content,which indicated that the crystalline structure of the SA film was disrupted by the addition of CL.In summary,the SA-CL films had a certain effect on the preservation of blueberries.With the increasing concentration of CL,the mechanical properties,water vapor transmission rate and thermal stability of the film decreased,while contact angle and water solubility increased.At the same time,due to the special amphiphilic structure of CL,the crystal properties of SA were destroyed,thus reducing the mechanical strength of the composite film,which made the composite film easier to clean.Therefore,this study is the first to combine CL and SA to prepare a berry fresh-keeping coating film that is suitable for fragile surfaces,which provided a new method for berry fresh-keeping and had important application value. |
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